Abel Electronics IO 32

[Loonhaunt]

Does anyone have experience with this expansion board. I have never used one. I just completed the soldering necessary to utilize the two 2 x 8 headers. I was hoping to get a clarification of why and when to use the INT A,B Pins, and how best to wire them, to what. Perhaps I should be asking for a good resource for I2C theory??

[Douglas6]

The definitive source will be the MCP23017 datasheet, but I might be able to give some background. Each MCP23017 on that board has two 'ports' of 8 GPIO pins. Each port also has an interrupt pin, INTA or B. This pin can be configured to go high when any of the port's GPIOs are triggered. And it will stay high until cleared (by reading the port latch register if I recall correctly.) So, a couple of advantages. One, you can poll a single pin to find out if any one (well, at least one) of eight pins was triggered. Two, because it 'latches', you wont miss a quick pin event that occurs while you are off doing other things, like polling other pins. Whether or not you need this is up to you, I'd say that often simply polling all 8 pins on each port in turn will work.

The interrupts can be configured per port for the event type (rising edge, falling edge, etc.) and you can also 'mask' off any of the GPIOs.